Process for optimizing milk production

ABSTRACT

A method of supplying a ruminant with its nutritional requirements for methionine is provided wherein an ester of 2-hydroxy-4(methylthio)butanoic acid that is available for absorption by a ruminant is administered to the ruminant. Preferably, the ruminant is administered an ester of 2-hydroxy-4(methylthio)butanoic acid is selected from the group consisting of methyl, ethyl, butyl, and 3-methylbutyl, and salts thereof.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Ser. No. 09/990,677, filed Nov. 16, 2001, which isa continuation of U.S. application Ser. No. 09/697,235, filed Oct. 26,2000, which is now U.S. Pat. No. 6,319,525, which is a continuation ofU.S. application Ser. No. 09/033,095, filed Jun. 15, 1999, which is nowU.S. Pat. No. 6,183,786, which is a continuation of U.S. applicationSer. No. 08/900,414, filed Jul. 25, 1997, now U.S. Pat. No. 6,017,563,the entire disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention generally relates to a process for satisfying thenutritional requirements of ruminants for methionine, and morespecifically, to a process for meeting those nutritional requirementsusing the hydroxy analog of methionine (2-hydroxy-4(methylthio)butanoicacid) and its salts, amides and esters.

High producing dairy cows need methionine, lysine and other keyessential amino acids to reach their genetic potential for milkproduction. While amino acids can be added directly to the diets ofmonogastric animals to overcome nutritional deficiencies, free aminoacids are rapidly degraded by rumen bacteria and are of little or nopractical benefit in alleviating amino acid deficiencies in ruminants.

Traditionally, undegradable intake protein (“UIP”) such as blood meal,fish meal, corn gluten meal and others have been used to provideessential amino acids to ruminants. It is difficult, however, toaccurately deliver needed levels of methionine and other essential aminoacids without providing excess levels of other non-essential amino acidsand, any excess nitrogen which UIP delivers to the rumen must bedegraded and eliminated by the animal. Consequently, formulating feedswhich satisfy the methionine requirements using UIP sources is not onlyexpensive, it can also affect cow health and productive status.

As an alternative to UIP, attempts have been made to modify or protectmethionine in a manner so that it is not susceptible, or at least isless susceptible, to rumen degradation. Various “coatings” formethionine have been proposed which, in theory, enable the rumenprotected methionine (“RPM”) to clear or “bypass” the rumen withoutsignificant destruction by rumen microflora and deliver this key aminoacid to the small intestine. Once in the small intestine, the coatingdissolves thereby freeing the methionine which is absorbed from theintestine.

The practical application of rumen protected methionine, however, haspresented some challenges. For example, some products have limitedsolubility. For others, pelleting, expander conditioning, mixing, andother normal milling practices fracture the protective coating, makingthe methionine molecule vulnerable to rumen degradation. Some dairyproducers have circumvented this problem by top dressing the rumenprotected methionine on final rations. This labor intensive practice,however, does not allow the ingredient to be uniformly distributed inthe diet. As a result, cows within a herd may consume different amountsof methionine.

It has been reported that the milk production of dairy cows can beincreased by supplementing the diets of the cows with the hydroxy analogof methionine and its salts and esters. See, e.g., U.S. Pat. No.4,388,327. Previous attempts to implement this technology, however, weremet with unpredictable milk production responses.

More recently, the calcium salt and the free acid forms of the hydroxyanalog of methionine have been combined with bypass fats in a dryproduct for use as an ingredient of a ruminant food ration. Asunderstood, the level of inclusion of the bypass fat/hydroxy analog dryproduct has been determined using a computer model which matches thenutritional requirements of the ruminant with available feedingredients. This approach, however, suffers from several disadvantages.Because the two ingredients are combined in a predetermined ratio, theproduct offers less flexibility in formulating a ration which meets aleast cost objective and precludes the possibility of formulating a feedration which includes the hydroxy analog of methionine but not bypassfat. In addition, the dry form of the product is susceptible to theformation of undesirable dust and to non-uniform mixing with other feedration ingredients.

SUMMARY OF THE INVENTION

Among the objects of the invention, therefore, is the provision of aprocess for satisfying the nutritional requirements of ruminants formethionine, the provision of such a process in which it is unnecessaryto coat or otherwise protect the methionine source from rumenmicroflora, the provision of such a process in which a predictable milkresponse is obtained, the provision of such a process which avoidsproviding excess levels of fats or other non-essential amino acids tothe ruminant in order to satisfy the methionine needs, and the provisionof such a process in which some of the UIP in a balanced ration may bereplaced with a lower cost source of methionine to yield a costimprovement.

Briefly, therefore, the present invention is directed to a process forformulating a ruminant food ration for a ruminant. In this process, themethionine needs of the ruminant are determined. A plurality of naturalor synthetic feed ingredients and the nutrient composition of each ofsaid ingredients is identified wherein one of said ingredients is2-hydroxy-4-(methylthio)butanoic acid or a salt, amide or ester thereof.From the identified feed ingredients, a ration is formulated to meet thedetermined methionine needs of the ruminant which comprises one or moregrains, a hydroxy analog of methionine, and optionally a bypass fatwherein (i) the hydroxy analog of methionine is selected from the groupconsisting of 2-hydroxy-4-(methylthio)butanoic acid and the salts,amides and esters thereof, (ii) the hydroxy analog of methionine isadded separately from any bypass fat which is included in the ration,and (iii) the ration is formulated on the basis that at least 20% of thehydroxy analog of methionine is assumed to be available for absorptionby the ruminant.

Other objects and features of this invention will be in part apparentand in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of HMB (DL, 2-hydroxy-4-[methylthio]butanoic acid)versus time for the study of Example 1.

FIG. 2 is a graph of HMB (DL, 2-hydroxy-4-[methylthio]butanoic acid)concentration in the duodenum versus time for the study of Example 1.

FIG. 3 is a graph of chromium concentration in the rumen versus time forthe study of Example 1.

FIG. 4 is a graph of chromium concentration in the duodenum versus timefor the study of Example 1.

FIG. 5 is a graph showing rumen and duodenal HMB (DL,2-hydroxy-4-[methylthio]butanoic acid) and serum methionine responsefollowing oral dosing of 90 g HMB in lactating dairy cows for the studyof Example 1.

FIG. 6 is a graph showing milk production (kg/d) versus time for thestudy of Example 2.

FIG. 7 is a graph showing fat percentage in milk versus time for thestudy of Example 2.

FIG. 8 is a graph showing fat corrected milk yield (kg/d) versus timefor the study of Example 2.

FIG. 9 is a graph showing protein percentage in milk versus time for thestudy of Example 2.

FIG. 10 is a graph showing milk production (lb./cow/day) versus time forthe study of Example 4.

FIG. 11 is a graph showing milk protein (lb./cow/day) versus time forthe study of Example 4.

FIG. 12 is a graph showing milk fat (lb./cow/day) versus time for thestudy of Example 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Optimizing milk production in ruminants requires matching thenutritional requirements of the ruminant with least cost sources fromavailable feed ingredients. In recent years, several computer modelshave been developed for this purpose; these models enable a dairynutritionist to predict the methionine and other nutrient requirementsfor high milk producing dairy cows and to formulate a feed ration usingleast cost sources. Two of the more well known models are the CornellNet Carbohydrate and Protein System (CNCPS) and the University ofPennsylvania DAIRYLP program. See, Fox, D. G., Using Computer Models inExtension to Develop More Profitable Feeding Systems, The National DairyDatabase, June 1992; Galligan, D. T., J. D. Ferguson, C. F. Ramberg, Jr.and W. Chalupa. 1986. Dairy Ration Formulation and Evaluation Programfor Microcomputers. J.Dairy Sci. 69:1656; Galligan, D. T., C. F.Ramberg, Jr., W. Chalupa and J. D. Ferguson. 1989. J.Dairy Sci. 72:suppl1):445. In general, the computer models use input data such as animaltype, body weight, fat test, milk production level, environmentalconditions, nutrient composition of available feeds, feed cost, andrumen bypass rates for degradable protein and amino acid sources. Fromthis information, the models formulate a least cost feed ration whichaccurately meets the ruminant's nutritional requirements to support thedesired level of milk production from available sources which typicallywill include corn, soy, alfalfa, vitamins, minerals, molasses, fatsources, amino acid sources, undegradable intake protein, and a varietyof other feedstuffs.

Depending upon the dose, location of administration and diet ormanagement factors, experimental evidence to date suggests that theamount of methionine hydroxy analog which bypasses the rumen and isavailable for absorption when the analog is fed to a ruminant in theabsence of a bypass fat is at least about 20% on a molecular basis.Experimental bypass data and field work with dairy cattle (based uponmilk response) further suggests that the amount which by-passes therumen is at least about 40% on a molecular basis. Additionalexperimental evidence suggests that about 8.8% of the analog is absorbedby the omasum and should be available for use. Still furtherexperimental evidence suggests that a certain percentage of methioninehydroxy analog which doesn't clear the rumen is actually absorbedthrough the rumen's epithelial lining. Everything considered, therefore,the amount of the hydroxy analog of methionine which bypasses the rumenand is available for absorption is between about 40% and about 55%.

In the process of the present invention, a conventional computer modelis used to determine the methionine and other nutritional requirementsof the ruminant and a least cost feed ration which will meet theserequirements is formulated. Advantageously, the feed ration includes thehydroxy analog of methionine and is formulated on the basis that atleast 20% of the hydroxy analog is assumed to be available forabsorption by the ruminant. Preferably, the ration is formulated on thebasis that at least about 40% of the hydroxy analog is assumed to beavailable for absorption by the ruminant and more preferably on thebasis that between about 40% and about 55% of the hydroxy analog isassumed to be available for absorption by the ruminant.

The hydroxy analog of methionine (“MHA”) which may be used in theprocess of the present invention include 2-hydroxy-4(methylthio)butanoicacid, its salts, esters, amides, and oligomers. Representative salts ofMHA include the ammonium salt, the stoichiometric andhyperstoichiometric alkaline earth metal salts (e.g., magnesium andcalcium), the stoichiometric and hyperstoichiometric alkali metal salts(e.g., lithium, sodium, and potassium), and the stoichiometric andhyperstoichiometric zinc salt. Representative esters of MHA include themethyl, ethyl, 2-propyl, butyl, and 3-methylbutyl esters of MHA.Representative amides of MHA include methylamide, dimethylamide,ethylmethylamide, butylamide, dibutylamide, and butylmethylamide.Representative oligomers of MHA include its dimers, trimers, tetramersand oligomers which include a greater number of repeating units.

In the dairy farm industry, dairy cows are fed as a ration, commonlyreferred to as a total mixed ration (TMR), which consists of a forageportion and a grain concentrate portion. The forage portion is typicallyprovided by the dairy farmer and generally consists of haylage orsilage, with the forage and grain concentrate portions being mixed bythe dairy farmer. The grain concentrate portion is typically prepared bya commercial feed mill and is generally prepared by mixing grains suchas corn, soy, and alfalfa with vitamins, minerals, molasses, fatsources, synthetic amino acids and a variety of other feedstuffs. Theseingredients are blended in commercial feed mills using conventionalmilling techniques which include augering, mixing, expanding, extruding,and pelleting.

In accordance with the present invention, the hydroxy analog ofmethionine is added separately and individually as an ingredient in thegrain concentrate portion of the ration; stated another way, the amountof hydroxy analog added to the grain concentrate portion of the rationis independent of the amount of bypass fat added (if any) to the grainconcentrate portion. Preferably, the hydroxy analog of methionine is thefree acid which is a liquid offering several handling and mixingadvantages. As a liquid, it is evenly absorbed by the grains and doesnot settle out of the mixture before consumption by the ruminant. Sinceits availability to the ruminant is not derived by any protectivecoating, it can be mixed, augered, exposed to high temperature steamconditioning, extruded, expanded or pelleted with no loss of productactivity. In addition, once consumed by the ruminant, the hydroxy analogof methionine is subject to no loss of activity resulting frommastication and cud chewing, as are calcium soaps of fatty acids (commonbypass fats), amino acids and other nutrients that derived theiractivity in the ruminant as a result of a protective coating.

In addition, the hydroxy analog of methionine which is incorporated intothe grain concentrate need not be coated with or incorporated into abypass fat in order to be available to the ruminant. This provides addedflexibility to allow the hydroxy analog of methionine to be added at thelevel required given the ration ingredients and the productivity of thecows receiving the ration.

In general, a bypass fat is a fat which has been chemically orphysically altered or synthesized to remain insoluble (or inert) as itpasses through the rumen of the cow. Bypass fats typically remain as asolid as they pass through the first parts of a ruminant's digestivetract including the rumen. After passing through the rumen, the fat issolubilized in the initial regions of the small intestine and thenbecomes available to enzymatic activity through well known mechanisms offat absorption. Some commercially available bypass fats are described,for example, in U.S. Pat. Nos. 5,182,126; 5,250,307; 5,391,787;5,425,963; and 5,456,927 which disclose C14-C22 fatty acids, theirglycerides, or their salts including, but not limited to, palmitic,oleic, linoleic, stearic, and lauric compounds. As used herein, however,the term bypass fat does not include fats of natural origin which arenormally present in the diet of a cow which include, but are not limitedto, animal fats such as poultry fat, animal tallow, animal oil, orvegetable oils such as canola oil, coconut oil, corn oil, cottonseedoil, palm oil, peanut oil, poultry fat, sunflower oil, soybean oil, orsafflower oil.

To derive benefit from addition of the hydroxy analog of methionine, oneneeds only verify that the ration fed at expected levels of consumption,is limiting in its content of available methionine. This is achievedthrough the use of computer models such as the CNCPS and DAIRYLP inconjunction with the supplementation of the appropriate level of thehydroxy analog of methionine, based on its availability in the ruminant.

As described in greater detail in the examples presented herein,research has confirmed that the hydroxy analog of methionine is readilyavailable as a methionine source for ruminant animals. This work hasconfirmed the rumen survivability of the hydroxy analog of methionineand its absorption, conversion, appearance in blood plasma as1-methionine and utilization for milk or muscle tissue. In particular,field trials have demonstrated that the hydroxy analog of methioninestatistically increased milk output versus control groups that wereverified to be methionine deficient through the use of computer models.In addition, when compared to other sources of rumen protectedmethionine, or methionine provided via various sources of undegradableintake protein, the hydroxy analog of methionine can be one of the mosteconomical means to provided needed methionine to the ruminant.Formulating a feed ration with the flexibility of being able to identifythe specific methionine needs of high producing cows from the methioninehydroxy analog instead of from UIP thus provides cost, herd health, andproduction advantages to the dairy farm industry.

The following examples will illustrate the invention.

EXAMPLE 1

Objective:

To determine the rumen bypass and gastrointestinal availability of HMB(DL, 2-hydroxy-4-[methylthio]butanoic acid) and the response of serummethionine to HMB supplementation in lactating dairy cows.

Experimental Procedures

The absorption and metabolism of 2-hydroxy-4-[methylthio]butanoic acidsold by Novus International (St. Louis, Mo. under the Alimet® wasmeasured in four lactating dairy cows fitted with rumen and duodenalT-type cannulae (10 cm distal to the pylorus). The cows were offered abasal diet of barley-based concentrate (Table I) and alfalfa hay. Theconcentrate was fed at a level of 1 kg for every 2.5 kg of milk produced(Table I) and access to alfalfa hay was ad libitum. In addition, cowsreceived 30 g HMB mixed with 2 kg ground corn grain per day for six daysto allow for adaptation of the rumen microflora. Cows were then fed 90 gHMB mixed with the ground corn and were administered 600 mlchromium-EDTA (3 g Cr) (Binnerts et al., “Soluble chromium indicatormeasured by atomic absorption in digestion experiments” Vet. Rec. (1968)page 470) into the rumen via the rumen cannula. The HMB meal was offeredto the cows for 20 minutes prior to the morning feeding and any of theremaining meal was placed in the rumen via the rumen cannula.

Blood, rumen and duodenal samples were collected at 0, 1, 3, 6, 9, 12and 24 hours post-HMB-feeding. Blood was collected by jugularveni-puncture into 2×10 ml sterile tubes (Vacutainer Brand SST tubes forserum separation, Bectin Dickenson, Rutherford, N.J.), allowed to standfor 30 minutes in an ice bath and centrifuged at 3000×g to separate theserum from cells. Serum was divided into two fractions. The firstfraction was deproteinized by adding an equal volume of acetonitrile andthen centrifuging to obtain the supernatant. The deproteinized serum wasthen frozen (−70° C.) until analysis. A second fraction was notdeproteinized but directly frozen (−70° C.). Rumen fluid (100 ml)collected from several sites within the rumen was strained through fourlayers of cheesecloth and subsampled. The subsample (30 ml) wasacidified with 6 M HCl (0.5 ml) and frozen (−40° C.). Duodenal samplescollected (100 ml) were also stored frozen (−40° C.). Rumen and duodenalsamples were later thawed and centrifuged at 23 000×g, 4° C., for 20minutes to obtain the clarified supernatant. The clarified rumen and theduodenal samples were then frozen until analysis. Serum was analyzed formethionine and rumen and duodenal samples for HMB. Chromium was measuredby atomic absorption spectrophotometry in rumen and duodenal samplesthat were diluted with an equal volume of a calcium chloride solution toyield samples with approximately 400 ppm Ca²⁺ (Williams et al., “Thedetermination of chromic oxide in faeces samples by atomic absorptionspectrophotometry” J. Agric. Sci., Vol. 59 (1962) pp. 381-385).

Results and Discussion

The cows refused to consume the 90 g HMB meal and, therefore, the mealwas placed in the rumen. The concentrations of Cr (liquid marker) andHMB in rumen and duodenal fluid for each of the four cows at varioustimes after intraruminal dosing is presented in Table II and FIGS. 1-4.When the data was plotted on a semilogarithmic scale (naturallogarithm), it followed a straight line (data not shown). The slope ofthe line from the semilogarithmic plot is equal to the fractional rateconstant (K). The rate constants were calculated by linear regression ofthe natural logarithm of Cr and HMB concentration verses time (TableIII). Regression analysis of rumen Cr concentration was performed withdata for 1 to 24 hours (excluding data for 0 hour). The rumenconcentration of HMB declined to levels below the detection limit of theanalytical technique (<10 ug/ml) by 24 hours and, therefore, regressionanalysis was performed with data for 1 to 12 hours (excluding data for 0and 24 hours).

Regression analysis for duodenal Cr and HMB concentration included thedata for 3 to 24 hours and 3 to 12 hours, respectively. Excluding thedata for 1 hour simplified the analysis by omitting the delay for thetranslocation of digesta from the rumen to the duodenum. Themathematical equations describing the decline of Cr and HMB in the rumen(R², 0.9855 and 0.9738, respectively) and duodenum (R², 0.9744 and0.9674, respectively) were well fitted to the data.

Assuming that the decline in rumen HMB concentration is due to thepassage of HMB from the rumen and microbial degradation of HMB withinthe rumen, then the fractional rate constant for HMB (−0.3269; TableIII) in the rumen will equal the sum of the rate constants for thepassage and degradation of HMB.K_([HMB−rumen])=K_([passage])+K_([degradation])

The HMB is soluble, and therefore, the rate at which HMB passes from therumen will be equivalent to the rate of passage for Cr, the liquidmarker (−0.1307). Thus, the rate constant for microbial degradationwithin the rumen is −0.1962(K_([HMB−rumen])−K_([passage])=K_([degradation])). The rumen degradationof HMB was determined based on the ratio of the rate of degradation ofHMB to the total rate of decline of HMB (−0.1962/−0.3269). Thus, 60%percent of the HMB dose disappeared in the rumen with 40% of the dosebypassing the rumen fermentation.

The fractional rate constant for the decline in HMB concentration at theproximal duodenum (−0.3380; Table III) is equal to the sum of the rateconstants for passage and disappearance of HMB.K_([HMB−duodenum])K_([passage])+K_([disappearance])

The rate constant for passage of HMB (K_([passage])) to the duodenum wasdetermined by calculating the rate constant for the passage of the Crmarker (−0.1053; Table III). Thus, 31.2% of the HMB fed to the cowspassed to the small intestine (−0.1053/−0.3380×100) and 68.8%disappeared [(−0.3380−(−0.1053))/−0.3380×100). The K for disappearanceat the duodenum includes the K for degradation in the rumen and the Kfor absorption postruminally but pre-intestinally (presumably theomasum).K_([disappearance])=K_([rumen degradation])+K_([omasal absorption])

It was determined from the rumen decline in HMB, that 60% of the HMBdisappeared in the rumen. Therefore, the remaining 8.8% of HMBdisappearance was due to omasal absorption. Of the original dose of HMBfed to the dairy cows, 60% was degraded in the rumen, 8.8% was absorbedin the omasum and 31.2% passed to the small intestine for absorption.While we have defined ruminal disappearance as degradation, thesubstantial quantity of omasal absorption of HMB indicates that it islikely that some fraction of the 60% ruminal disappearance may haveoccurred via absorption through the rumen wall. As HMB is absorbed viapassive diffusion in other species, it is reasonable to expect thisphenomenon to occur in rumen epithelium as well. Therefore, thebioavailability of 40% for HMB, as a methionine source for ruminants, islikely a conservative underestimate.

Peak concentrations for ruminal and duodenal HMB occurred at 1 and 3hours, respectively. Peak serum methionine concentration occurred at 6hours. By 12 hours, all values had returned to pre-dose levels (FIG. 5).The absorption of HMB from the omasum and small intestine and itssubsequent metabolism to methionine produced an increase in serummethionine of 200% above pre-dose levels at the peak concentration.TABLE I Composition of Concentrate Item Ingredient, % (as-fed basis)Barley grain (medium roll) 51 Rolled corn 10 Beet pulp 8.5 Blood meal11.5 Soybean meal 4.2 Canola meal 4 Canola oil 3.5 Liquid molasses 2Mineral premix¹ 2 Sodium bicarbonate 1.5 Dicalcium phosphate 1Perma-Pell 0.8 Vitamin ADE² 0.025 Flavor³ 0.017¹Supplies per kg of concentrate: Na, 0.7%; S, 0.2%; K, 0.02%; Mg. 0.01%;Zn, 154 mg/kg; Mn, 147 mg/kg; Cu, 40 mg/kg; 1, 2 mg/kg; Se, 0.8 mg/kg;and Co, 0.6 mg/kg.²Supplies per kg of concentrate: vitamin A, 2500 IU; vitamin D, 250 IU;and vitamin E 2.5 IU.³ACS Cattle feeding flavor, Alltech, Inc.

TABLE II Chromium and HMB Concentration in Rumen and Duodenal FluidChromium Concentration Time (ug/ml) HMB Concentration (ug/ml) (h) 124131 133 138 124 131 133 138 Rumen 0 0.04 0.07 0.01 0.02 <10 <10 <10 <101 31.83 36.27 40.44 45.51 538.6 615.1 766.6 875.8 3 23.77 29.11 34.5237.05 326.7 401.1 539.1 656.3 6 19.29 18.09 16.62 27.94 209.9 170.3173.4 342.0 9 12.93 8.89 10.79 13.89 78.6 50.8 59.3 94.0 12 9.16 5.047.86 8.28 22.1 13.2 22.8 19.7 24 3.62 1.07 2.08 1.97 <10 <10 <10 <10Duodenum 0 1.36 0.05 0.05 0.02 <10 <10 <10 <10 1 11.69 23.80 12.14 17.98159.3 370.6 189.2 336.8 3 18.30 24.55 25.41 27.23 245.5 324.5 367.5477.8 6 11.99 17.86 18.42 23.24 81.7 146.2 169.8 276.3 9 11.00 12.1616.36 19.26 40.6 47.1 70.3 142.7 12 7.89 6.39 7.89 8.39 11.6 13 15.125.4 24 3.88 2.06 2.29 2.85 <10 <10 <10 <10

TABLE III Linear Regression Analysis of the Natural Logarithm of Cr andHMB Concentration in Rumen and Duodenal Fluid Verses Time Chromium HMBCow Constant K R² Constant K R² Rumen 1 to 24 hours 1 to 12 hours  243.4702 −.0940 .9883 6.7179 −.2809 .9654 131 2.7330 −.1576 .9878 6.9865−.3506 .9835 133 3.7310 −.1302 .9781 7.1155 −.3317 .9940 138 3.9905−.1411 .9877 7.4596 −.3444 .9524 Mean 3.7312 −.1307 .9855 7.0699 −.3269.9738 SD 0.2124 .0270 .0049 .3081 .0317 .0185 Fitted Y =41.7292e^(−.1307t) Y = 1176.0304e^(−.3269t) Equation Duodenum 3 to 24hours 3 to 12 hours 124 3.0038 −.0705 .9747 6.4793 −.3285 .9895 1313.5284 −.1201 .9823 6.9923 −.3595 .9895 133 3.6342 −.1173 .9796 7.1167−.3486 .9713 138 3.7419 −.1135 .9608 7.3626 −.3155 .9194 Mean 3.4771−.1053 .9744 6.9877 −.3380 .9674 SD .3273 .0234 .0096 .3722 .0198 .0331

EXAMPLE 2

In a lactation study, the effects of providing Alimet®(2-hydroxy-4-[methylthio]butanoic acid sold by Novus International (St.Louis, Mo.)) feed supplement in the close-up pre-lactation dry periodand in early lactation diets was evaluated. The diets (Table IV) wereformulated to include Alimet® to meet the methionine requirements asdetermined using existing computer modeling technology (CNCPS andDAIRYLP). The diets were balanced to meet amino acid requirements andincluded standard feed ingredients used in dairy rations. In the absenceof added Alimet®, the control diet was predicted to be first limiting inmethionine. The estimated need for methionine was approximately 9 gramsper day. Alimet® was added assuming an availability to the ruminant of20%.

This study included 10 multiparous and five primiparous cows pertreatment, supplemented with Alimet® for two weeks before calving andfor 12 weeks of lactation. The Alimet® treatment group produced moremilk (33.9 vs 31.3 kg/d; FIG. 6) with a higher fat content (4.01% vs3.71%; FIG. 7) than unsupplemented cows. This resulted in morefat-corrected content (FCM) production for the Alimet-fed cows (33.4 vs29.2 kg/d; FIG. 8) but not milk protein content (FIG. 9). At peak milkyield, Alimet-fed multiparous cows produced 7.9 kg/d more FCM thanunsupplemented cows (42.0 vs 34.1 kg/d). The benefits of supplying postruminal amino acid would appear to be greatest during the close-up dryperiod and early lactation. TABLE IV Basal Ration* Barley  27%Cottonseed  11% Soy bean meal 6.3% Corn distillers grain 8.0% Blood meal2.0% Megalac (bypass fat) 2.0% Alfalfa haylage  24% Alfalfa hay  17%*Standard basal diet without Alimet ®

EXAMPLE 3

In a field trial, Alimet® (2-hydroxy-4-[methylthio]butanoic acid sold byNovus International (St. Louis, Mo.) at a 40% bypass estimate) was fedto 75 high producing early lactation cows as part of their diet. TheCornell Net Carbohydrate Net Protein Model was used to evaluate the diet(corn grain based diet) being fed to these cattle. The ration being fedwas balanced for 90 pounds of 3.7% butterfat milk per cow per day. Inthe absence of added Alimet®, the diet was predicted to be firstlimiting in methionine.

Seventy five multiparous cows were used in each group. The cows werehoused in either side of a modern, well ventilated free stall barn.Cattle were allocated to treatment by calving date. As cows calved theywere alternately placed in the Alimet® group or a group fed the samecommercial TMR without Alimet®. This commercial TMR represents thestandard TMR fed in the field at commercial dairies at that time. Milkproduction of each cow was measured at every milking until 75 cows hadbeen on Alimet® for approximately 90 days and 75 cows had been on thecontrol TMR for about 90 days.

The statistical model used was for a completely randomized design. Thisdesign is established by assigning treatments at random to a previouslyselected set of experimental units. In this case, the treatments wereAlimet® or no Alimet®, and the experimental units were cows that werefreshening. Assignment to treatment was completely randomized since itwas based on calving order. As previously mentioned, cows were placedalternately into the Alimet® group or treatment group as they calved.The data were analyzed with a one way Analysis of Variance procedure,using the F test to determine statistical differences.

The data indicate that the cows receiving Alimet® produced over 5 poundsmore milk per cow per day during the period of the trial. Thisproduction response was significant at the P<0.04 level (Table V). Onecow was excluded from the control group due to extremely low milkproduction, therefore only 74 cows were used for statistical analysis.The last cow to complete the 90 days of Alimet® feeding was not used inorder to balance cow numbers across treatments. This cow averaged 90pounds of milk per day. There was no significant difference in days inmilk of cows in either group when the trial was concluded.

In conclusion, this data set shows that Alimet® provides an acceptablesource of bypass methionine in high producing, early lactation cows,when fed from the beginning of lactation onward, to cows consuming acorn silage based diet. TABLE V ANOVA Source of Variation SS df MS FP-value F crit Between Groups 935.5762848 1 935.5763 4.312277 0.0395913.905939 Within Groups 31675.6377 146 216.9564 Total 32611.21399 147Conclusion:

Trial compared two groups of early lactation cows. One group was fedAlimet® and the other was not. The diets were isonitrogenous; theAlimet® diet crude protein level was adjusted to account for thenitrogen provided by the treatment. Both diets were fed as Total MixedRations on an ad libitum basis.

The data indicate that the feeding of Alimet® resulted in an increase of5.03 pounds of milk per cow per day. This result is statisticallysignificant at the P 0.0396 level.

EXAMPLE 4

In a field trial, Alimet® (2-hydroxy-4-[methylthio]butanoic acid sold byNovus International (St. Louis, Mo.) at a 40% bypass estimate) was fedto 600 cows of a 1900 cow commercial dairy as part of their standard,commercial ration. Computer models were used to determine methioninedeficiency and to balance the ration for Alimet® inclusion. The sixhundred cows consumed an average of 3.8 grams of Alimet® per head perday over a 102 day feeding period. In the absence of added Alimet®, thecontrol diet was predicted to be first limiting in methionine. TheAlimet® supplemented cows produced an average of 2.67 lb. (1.21 kg) moremilk per cow daily. Milk protein yield averaged 0.22 lb. (99.8 g) moreper cow daily. Milk fat yield averaged 0.26 lb. (118 g) more per cowdaily.

FIGS. 10-12 summarize the data. It should be noted that the supplementbegan on the sixth day of month 1 and ended on the fifteenth day ofmonth 4.

In the view of the above, it will be seen that the several objects ofthe invention are achieved.

As various changes could be made in the above compositions and processeswithout departing from the scope of the invention, it is intended thatall matter contained in the above description be interpreted asillustrative and not in a limiting sense.

1. A method of supplying a hydroxy analogue of methionine that isavailable for absorption to a dairy cow, comprising administering to thecow an ester of 2-hydroxy-4(methylthio)butanoic acid, wherein the esteris selected from the group consisting of methyl, ethyl, butyl, and3-methylbutyl, and salts thereof.
 2. The method of claim 1, wherein theester of 2-hydroxy-4(methylthio)butanoic acid comprises the methyl esterof 2-hydroxy-4(methylthio)butanoic acid.
 3. The method of claim 1,wherein the ester of 2-hydroxy-4(methylthio)butanoic acid comprises theethyl ester of 2-hydroxy-4(methylthio)butanoic acid.
 4. The method ofclaim 1, wherein the ester of 2-hydroxy-4(methylthio)butanoic acidcomprises the butyl ester of 2-hydroxy-4(methylthio)butanoic acid. 5.The method of claim 1, wherein the ester of2-hydroxy-4(methylthio)butanoic acid comprises the 3-methylbutyl esterof 2-hydroxy-4(methylthio)butanoic acid.
 6. The method of claim 1,wherein at least 20% of the ester of the 2-hydroxy-4(methylthio)butanoicacid is available for absorption by the cow.
 7. The method of claim 1,wherein at least 40% of the ester of the 2-hydroxy-4(methylthio)butanoicacid is available for absorption by the cow.
 8. The method of claim 1,wherein between about 40% and about 55% of the ester of the2-hydroxy-4(methylthio)butanoic acid is available for absorption by thecow.
 9. The method of claim 1, wherein the ester of2-hydroxy-4(methylthio)butanoic acid is administered to the cow byfeeding the cow a feed comprising the ester of2-hydroxy-4(methylthio)butanoic acid.
 10. The method of claim 9, whereinthe feed is a ruminant feed ration.
 11. The method of claim 10, whereinthe feed ration comprises a grain portion.
 12. The method of claim 10,wherein the feed ration comprises a forage portion.
 13. The method ofclaim 12, wherein the forage portion is selected from haylage andsilage.
 14. A method of improving milk, the method comprisingadministering to a dairy cow an ester of 2-hydroxy-4(methylthio)butanoicacid, wherein the ester is selected from the group consisting of methyl,ethyl, butyl, and 3-methylbutyl, and salts thereof.
 15. The method ofclaim 14, wherein the milk improvement comprises increased milk proteincontent.
 16. The method of claim 14, wherein the milk improvementcomprises increased milk fat content.
 17. The method of claim 14,wherein the milk improvement comprises increased milk volume.
 18. Themethod of claim 14 wherein at least 20% of the ester of the2-hydroxy-4(methylthio)butanoic acid is available for absorption by thecow.
 19. The method of claim 14 wherein at least 40% of the ester of the2-hydroxy-4(methylthio)butanoic acid is available for absorption by thecow.
 20. The method of claim 14 wherein between about 40% and about 55%of the ester of the 2-hydroxy-4(methylthio) butanoic acid is availablefor absorption by the cow.
 21. A ruminant feed ration comprising: aplurality of natural or synthetic feed ingredients which comprises oneor more grains; and an ester of 2-hydroxy-4(methylthio)butanoic acid;wherein the ester is selected from the group consisting of methyl,ethyl, butyl, and 3-methylbutyl, and salts thereof.
 22. The ruminantfeed ration of claim 21, wherein the feed ingredients further comprise aforage portion.
 23. The ruminant feed ration of claim 21, wherein theforage portion is selected from haylage and silage.